linux-kernel - Re: [PATCH] hwmon: (gpio-fan) Remove un-necessary speed

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Date:	Fri, 19 Feb 2016 17:15:20 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Nishanth Menon <nm@...com>, Jean Delvare <jdelvare@...e.com>
Cc:	Tony Lindgren <tony@...mide.com>, linux-kernel@...r.kernel.org,
	lm-sensors@...sensors.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Eduardo Valentin <edubezval@...il.com>
Subject: Re: [PATCH] hwmon: (gpio-fan) Remove un-necessary speed_index lookup
 for thermal hook

On 02/19/2016 04:09 PM, Nishanth Menon wrote:
> Thermal hook gpio_fan_get_cur_state is only interested in knowing
> the current speed index that was setup in the system, this is
> already available as part of fan_data->speed_index which is always
> set by set_fan_speed. Using get_fan_speed_index is useful when we
> have no idea about the fan speed configuration (for example during
> fan_ctrl_init).
>
> When thermal framework invokes
> gpio_fan_get_cur_state=>get_fan_speed_index via gpio_fan_get_cur_state
> especially in a polled configuration for thermal governor, we
> basically hog the i2c interface to the extent that other functions
> fail to get any traffic out :(.
>
> Instead, just provide the last state set in the driver - since the gpio
> fan driver is responsible for the fan state immaterial of override, the
> fan_data->speed_index should accurately reflect the state.
>
> Fixes: b5cf88e46bad ("(gpio-fan): Add thermal control hooks")
>
> Reported-by: Tony Lindgren <tony@...mide.com>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: Eduardo Valentin <edubezval@...il.com>
> Signed-off-by: Nishanth Menon <nm@...com>
> ---

Applied.

Thanks,
Guenter

> Test logs from linus master  v4.5-rc4-137-g23300f657594
> Without fix: http://paste.ubuntu.org.cn/3948618
> With Fix: http://paste.ubuntu.org.cn/3948617
>
>   drivers/hwmon/gpio-fan.c | 7 +------
>   1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
> index 82de3deeb18a..685568b1236d 100644
> --- a/drivers/hwmon/gpio-fan.c
> +++ b/drivers/hwmon/gpio-fan.c
> @@ -406,16 +406,11 @@ static int gpio_fan_get_cur_state(struct thermal_cooling_device *cdev,
>   				  unsigned long *state)
>   {
>   	struct gpio_fan_data *fan_data = cdev->devdata;
> -	int r;
>
>   	if (!fan_data)
>   		return -EINVAL;
>
> -	r = get_fan_speed_index(fan_data);
> -	if (r < 0)
> -		return r;
> -
> -	*state = r;
> +	*state = fan_data->speed_index;
>   	return 0;
>   }
>
>